CN102790201B - Lithium ion cell positive and lithium ion battery - Google Patents

Abstract

The invention provides a lithium ion battery positive pole, wherein the lithium ion battery positive pole is composed of a lithium ion battery positive pole active material and a conductive carrier, and the conductive carrier includes a plurality of carbon nanotubes. Since the lithium ion battery positive electrode provided by the present invention does not require a binder, the specific gravity of the lithium ion battery positive electrode active material in the lithium ion battery positive electrode can be further improved. The overall conductivity of the positive electrode of the battery will also be improved accordingly. The present invention further provides a lithium ion battery using the positive electrode of the above lithium ion battery.

Description

Lithium-ion battery positive electrode and lithium-ion battery

technical field

The invention relates to a positive pole of a lithium ion battery and a lithium ion battery using the positive pole of the lithium ion battery, in particular to a positive pole of a lithium ion battery and a battery based on carbon nanotubes.

Background technique

Lithium-ion battery is a new type of green chemical power source. Compared with traditional nickel-cadmium batteries and nickel-hydrogen batteries, it has the advantages of high voltage, long life, and high energy density. Since Japan's Sony Corporation launched the first generation of lithium-ion batteries in 1990, it has developed rapidly and is widely used in various portable devices.

Lithium-ion battery positive electrodes generally include positive electrode materials and conductive particles. The positive electrode material is mainly composed of a positive electrode active material. Cathode active materials generally use intercalation compounds, such as lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, etc. The active materials of other positive electrode materials also include iron oxides and other metal oxides. Conductive particles are generally particles with good conductivity. Graphite, acetylene black and carbon fiber have the characteristics of good conductivity, low density, stable structure and stable chemical properties, and are often used as conductive agents for lithium-ion battery cathode materials. There are two structures of the positive electrode of lithium-ion batteries, one is to form a fixed shape of positive electrode material and conductive particles directly as the positive electrode of lithium-ion batteries, and the other is to coat or fix the positive electrode material and conductive particles on a current collector. have to. Regardless of the structure of the lithium-ion battery positive electrode, since the lithium-ion battery positive electrode active material and conductive particles are non-adhesive powders, when forming them into a fixed shape or coating and fixing them on the current collector, a binder is required to The lithium-ion battery positive electrode powder and conductive particles are bonded together to form a lithium-ion battery positive electrode with a fixed shape. The binder is usually an organic material, including polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) or styrene-butadiene rubber (SBR), etc. The weight ratio of the binder in the positive electrode of the lithium-ion battery is generally about 10%. Because these binder materials do not possess conductivity, the addition of the binder affects the conductivity of the positive electrode of the lithium ion battery, and the binder occupies a certain volume and weight in the positive electrode of the lithium ion battery, making the positive electrode of the lithium ion battery Lower specific capacity.

Contents of the invention

Therefore, it is indeed necessary to provide a lithium ion battery positive electrode without binder and a battery using the positive electrode.

A lithium ion battery positive pole, the lithium ion battery positive pole is composed of a lithium ion battery positive pole active material and a conductive carrier, the conductive carrier includes a plurality of carbon nanotubes.

Compared with the prior art, the positive electrode of the lithium ion battery provided by the present invention does not require a binder, and the specific gravity of the positive electrode active material of the lithium ion battery in the positive electrode of the lithium ion battery can be further improved. With the barrier of the insulating material, the overall conductivity of the positive electrode of the lithium-ion battery will also be improved accordingly.

Description of drawings

FIG. 1 is a scanning electron micrograph of a section of the positive electrode of a lithium-ion battery provided by the present invention.

FIG. 2 is a schematic diagram of FIG. 1 .

Fig. 3 is a scanning electron micrograph of the positive electrode active material of lithium cobalt oxide in the positive electrode of the lithium ion battery provided by the present invention.

Fig. 4 is a transmission electron micrograph of the carbon nanotubes in the positive electrode of the lithium ion battery provided by the present invention.

Fig. 5 is a graph comparing the stress-strain curves of the positive electrode of the lithium ion battery provided by the present invention and the positive electrode of the lithium ion battery containing a binder.

Fig. 6 is a graph comparing the cycle performance of the lithium ion battery using the positive electrode of the lithium ion battery provided by the present invention with the cycle performance of the lithium ion battery using the positive electrode of the lithium ion battery added with a binder.

Fig. 7 is a comparison chart of the rate performance of the lithium ion battery using the positive electrode of the lithium ion battery provided by the present invention and the rate performance of the lithium ion battery using the positive electrode of the lithium ion battery added with a binder.

Fig. 8 is a side sectional view of the lithium ion battery provided by the present invention.

Explanation of main component symbols

Li-ion battery cathode 10 Positive electrode active material particles 14 carbon nanotubes 12 Lithium Ion Battery 100 case 20 negative electrode 30 Electrolyte 40 diaphragm 50 positive terminal 102 negative terminal 302

The following specific embodiments will further illustrate the present invention in conjunction with the above-mentioned drawings.

detailed description

The embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Referring to FIG. 1 and FIG. 2 , an embodiment of the present invention provides a positive electrode 10 of a lithium-ion battery. The positive electrode 10 of the lithium ion battery is composed of a plurality of positive electrode active material particles 14 and a plurality of conductive carriers. The plurality of conductive supports includes a plurality of carbon nanotubes 12 . The plurality of carbon nanotubes 12 are intertwined to form a network structure. The plurality of positive electrode active material particles 14 are attached to the surface of the carbon nanotubes 12 .

The material of the positive electrode active material particles 14 can be lithium iron phosphate (LiFePO ₄ ), lithium nickel cobalt (LiNi _0.8 Co _0.2 O ₂ ), lithium nickel cobalt manganese (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ) and lithium manganese oxide (LiMn ₂ O ₄ ). The shape of the positive electrode active material particles 14 is not limited, and may be regular or irregular. FIG. 3 is a scanning electron micrograph of pure positive electrode active material particles 14 . It can be seen from FIG. 3 that the particle diameter of positive electrode active material particles 14 is 100 nanometers to 100 microns. In this embodiment, lithium cobaltate is selected as the positive electrode active material, the positive electrode active material particles 14 are lithium cobaltate particles, and the particle diameter of the positive electrode active material particles 14 is less than 15 microns.

The conductive carrier may be all carbon nanotubes 12, or may include a mixture of carbon nanotubes 12 and conductive particles. The conductive particles include one or any mixture of graphite, acetylene black and carbon fiber. Regardless of whether the conductive carrier is composed of pure carbon nanotubes 12 or mixed with other conductive particles, the carbon nanotubes 12 are intertwined with each other or combined with each other through van der Waals force to form an overall network structure. The positive active material particles 14 are distributed in the network structure composed of carbon nanotubes 12, and most of the positive active material particles 14 are in contact with the carbon nanotubes. The positive active material particles 14 may be adhered or entangled by carbon nanotubes. When the conductive carrier also includes other conductive particles, the other conductive particles are uniformly mixed with the positive electrode active material 14 and distributed in the network structure composed of carbon nanotubes 12, that is, the network structure formed by the carbon nanotubes is integrally formed A fixed or solid structure. The carbon nanotubes 12 are not only used as conductive materials, but also as porous carriers. In this embodiment, all the conductive carriers are carbon nanotubes 12 , that is, the positive electrode 10 of the lithium ion battery is composed of a plurality of carbon nanotubes 12 and a plurality of positive electrode active material particles 14 . The carbon nanotubes 12 include single-wall carbon nanotubes, double-wall carbon nanotubes or multi-wall carbon nanotubes. The carbon nanotubes 12 have a diameter of 1 nanometer to 200 nanometers. Please refer to FIG. 4 . It can be seen from FIG. 4 that the surface of the carbon nanotubes 12 is relatively pure and there are basically no impurities. The lengths of the carbon nanotubes 12 may be equal or unequal. Preferably, the length of the carbon nanotubes 12 is greater than 300 microns, and the lengths of the carbon nanotubes 12 are equal. The mass percentage of the plurality of carbon nanotubes 12 in the positive electrode 10 of the lithium ion battery is greater than or equal to 0.1wt% and less than 10wt%, such as 0.1wt%, 1wt% or 5wt%. In this embodiment, preferably, the mass percentage of the plurality of carbon nanotubes in the positive electrode of the lithium-ion battery is less than or equal to 5 wt%. In the positive electrode of the lithium-ion battery, the mass percentage of the positive electrode active material is greater than or equal to 90wt% and less than or equal to 99.9wt%. Preferably, the mass percentage of the positive electrode active material is greater than or equal to 95wt% and less than or equal to 99.9wt%. Preferably, the plurality of carbon nanotubes 12 are evenly distributed in the lithium-ion battery and are isotropic. The isotropy means that the distribution density of the carbon nanotubes 12 in the positive electrode 10 of the lithium-ion battery is basically the same, that is, the mass percentage of the carbon nanotubes 12 in the lithium-ion battery 10 per unit volume is basically the same. Therefore, the resistivity of the positive electrode 10 of the lithium ion battery is uniform.

In the positive electrode 10 of the lithium ion battery, most of the positive electrode active material particles 14 are attached to the surface of the carbon nanotubes 12 or entangled by the carbon nanotubes 12 . Since the network structure composed of carbon nanotubes 12 is a porous structure, most of the positive electrode active material particles 14 are surrounded and fixed by the network structure. Preferably, a network structure composed of carbon nanotubes is evenly distributed throughout the positive electrode 10 of the lithium ion battery, that is, the positive electrode active material particles 14 are all located in the network structure composed of carbon nanotubes. The network structure covers or entangles the positive electrode active material particles 14 , and the carbon nanotubes 12 can play a role of binding the positive electrode active material particles 14 while serving as a conductive agent. Since the carbon nanotubes 12 have a relatively long length, generally greater than 200 microns, the carbon nanotubes 12 can be intertwined to form a network structure in the positive electrode 10 of the lithium-ion battery. In this way, the positive electrode active material particles 14 can be fixed together by the carbon nanotubes 12 . When the positive electrode 10 of the lithium ion battery includes other conductive particles, the other conductive particles may also be attached to the surface of the carbon nanotubes 12 or entangled by the carbon nanotubes 12 . Figure 5 is a graph comparing the stress-strain data of the positive electrode of a lithium-ion battery provided by an embodiment of the present invention with the strength of a positive electrode of a lithium-ion battery containing a PTFE binder. The positive electrode of the lithium ion battery in this embodiment is composed of lithium cobalt oxide particles and carbon nanotubes, and the weight ratio of lithium cobalt oxide particles and carbon nanotubes is 8:0.2. The positive electrode of lithium ion battery containing PTFE binder is composed of lithium cobaltate particles, carbon black and PTFE, and the mass ratio of lithium cobaltate particles, carbon black and PTFE is 8:0.5:1. Since the strength of the material is equal to the maximum stress value in the stress curve, it can be seen from Fig. 5 that the strength of the positive electrode 10 of the lithium ion battery provided by the present invention is much higher than that of the positive electrode of the lithium ion battery containing the PTFE binder, and can be It is proved that although the positive electrode 10 of the lithium ion battery provided by the present invention does not add a binder material, the strength of the positive electrode 10 of the lithium ion battery can still meet the actual needs.

The following will test and compare the performance of the lithium-ion battery positive electrode (No. 1 positive electrode) provided by the present invention and a lithium-ion battery positive electrode (No. 2 positive electrode) commonly used in the prior art. Both the No. 1 positive electrode and the No. 2 positive electrode are circular electrode sheets formed by punching. Their test dimensions are both 7 mm in diameter and 0.34 mm in thickness. The active material of the positive electrode of the lithium-ion battery is lithium cobalt oxide. The composition of positive electrode No. 1 is lithium cobalt oxide particles and carbon nanotubes, wherein the mass ratio of lithium cobalt oxide particles and carbon nanotubes is 8:0.2. The composition of positive electrode No. 2 is lithium cobalt oxide particles, carbon black and PTFE bonded agent, and its mass ratio is 8:0.2:1. The performance test and comparison of No. 1 positive electrode and No. 2 positive electrode are as follows:

The resistivity of No. 1 positive electrode is 0.89×10 ^-3 ohm·m (Ω·m), and the resistivity of No. 2 positive electrode is 491×10 ^-3 ohm·m (Ω·m). It can be seen that the conductivity of No. 1 positive electrode without binder is much higher than that of No. 2 positive electrode with binder added. This is because, compared with the No. 2 positive electrode, since no binder is added to the No. 1 positive electrode, there is no barrier of insulating substances between the positive electrode active materials of the lithium-ion battery, and the overall conductivity of the positive electrode of the lithium-ion battery will be improved accordingly.

Please refer to Fig. 6. Compared with No. 2 positive pole and No. 1 positive pole, the cycle performance of No. 1 battery is far better than that of No. 2 battery when discharging more than 20 times. It can be seen that the lithium ion battery provided by the present invention has better positive cycle performance.

Please refer to Figure 7, the cycle performance of No. 1 positive electrode and No. 2 positive electrode is basically the same in the case of low rate discharge (0.1C), but in the case of high rate discharge (1C and 2C), the cycle performance of No. 1 positive electrode Significantly higher than No. 2 positive pole. It can be seen that the No. 1 cathode has better charge-discharge performance at high rates.

The total weight specific capacity of the No. 1 positive electrode is 146.6mah/g, and the total weight specific capacity of the No. 2 positive electrode is 132.2mah/g, that is, the total weight specific capacity of the No. 1 positive electrode is greater than that of the No. 2 positive electrode.

From the above performance comparisons, it can be seen that the positive electrode of the lithium ion battery provided by the present invention has stronger electrical conductivity and better charge and discharge performance at high rates than the positive electrode of the traditional lithium ion battery. Further, since the middle part of the positive electrode of the lithium ion battery provided by the present invention does not include the weight of the binder, under the same total weight of the positive electrode of the lithium ion battery, the weight of the positive active material can be increased by 10% relative to the positive electrode of the traditional lithium ion battery. %above. In other words, under the condition of the same specific capacity and total capacity, the lithium ion battery provided by the present invention constitutes a battery having a smaller mass.

It can be understood that a small amount of carbon black can be further included in the positive electrode of the lithium ion battery provided by the present invention, that is, the positive electrode of the lithium ion battery includes carbon nanotubes and carbon black at the same time, and the mass percentage of the carbon black in the positive electrode of the lithium ion battery Less than 2%, preferably less than or equal to 1wt%, the mass percentage of the carbon nanotubes in the positive electrode of the lithium ion battery is greater than or equal to 0.1wt% and less than 10wt%. When the lithium-ion battery positive electrode includes a small amount of carbon black, because carbon black exists in the form of particles, and carbon nanotubes are continuous linear materials, carbon black particles can be better filled between carbon nanotubes and lithium-ion battery positive electrode active materials. Between or between the positive electrode active material particles of the lithium ion battery, the conductivity of the positive electrode of the lithium ion battery is further improved, and the specific capacity of the lithium ion battery is increased.

Since the lithium ion battery positive electrode provided by the present invention does not require a binder, the specific gravity of the lithium ion battery positive electrode active material in the lithium ion battery positive electrode can be further improved. The overall conductivity of the positive electrode of the battery will also be improved accordingly. Moreover, since the binder is generally an organic substance, which pollutes the environment, the lithium-ion battery of the present invention does not need a binder and is more environmentally friendly.

Please refer to FIG. 8 , the present invention further provides a lithium ion battery 100 using the positive electrode of the above lithium ion battery, which includes: a casing 20 and a lithium ion battery positive electrode 10 placed in the casing 20, a negative electrode 30, and an electrolyte 40 and diaphragm 50 . In the lithium ion battery 100, the electrolyte 40 is placed in the casing 20, the positive electrode 10, the negative electrode 30 and the separator 50 of the lithium ion battery are placed in the electrolyte 40, and the separator 50 is placed between the positive electrode 10 and the negative electrode 30 of the lithium ion battery. The inner space of the casing 20 is divided into two parts, and the positive electrode 10 and the separator 50 of the lithium ion battery and the negative electrode 30 and the separator 50 are spaced apart. The positive electrode terminal 102 and the negative electrode terminal 302 are respectively connected to tops of the positive electrode 10 and the negative electrode 30 .

When charging, the potential applied to the two poles of the lithium-ion battery 100 forces the active material in the positive electrode 10 of the lithium-ion battery to release lithium ions and electrons, and the lithium ions are embedded in the carbon of the graphite structure in the negative electrode 30, and the graphite structure simultaneously obtains a Electronics; during discharge, lithium ions and electrons are separated from the graphite-structured carbon of the negative electrode 30, and the lithium ions are combined with the active material in the positive electrode 10 of the lithium-ion battery, and the active material obtains an electron at the same time. Since the positive electrode of the lithium ion battery does not need a binder, in the positive electrode 10 of the lithium ion battery, the content of the active material of the positive electrode of the lithium ion battery is relatively high, and the overall conductivity of the positive electrode 10 of the lithium ion battery will also be improved accordingly. The lithium ion battery 10 composed of the positive electrode 10 has good cycle performance and large specific capacity.

The structure of the lithium-ion battery is not limited to the above-mentioned structure, as long as the lithium-ion battery is used in the positive electrode of the lithium-ion battery disclosed in the present invention, it is within the protection scope of the present invention.

It can be understood that when the positive electrode active material adopts materials containing other metal ions, the positive electrode can also be the positive electrode of other metal ions, such as the positive electrode of a potassium ion battery, as long as carbon nanotubes are added to the positive electrode to form a network structure for fixing the positive electrode active material. within the scope of the present invention.

In addition, those skilled in the art can also make other changes within the spirit of the present invention. Of course, these changes made according to the spirit of the present invention should be included within the scope of protection claimed by the present invention.

Claims (12)

1. a lithium ion cell positive, it is characterised in that this lithium ion cell positive is lived by lithium ion cell positive Property material and conductive carrier composition, this conductive carrier is to be wound around mutually or logical between multiple CNT Cross Van der Waals force to be combined with each other, and the network structure of form a entirety, described positive electrode active materials divides Cloth is adhered to by CNT in the network structure that CNT forms or is wound around, and described CNT is long Degree is more than 200 microns, and weight/mass percentage composition in lithium ion cell positive for the described CNT is more than It is less than 10wt% in 0.1wt%.

2. lithium ion cell positive as claimed in claim 1, it is characterised in that described cathode active material bag Include one or more in LiFePO4, lithium nickel cobalt, lithium nickel cobalt manganese, cobalt acid lithium, lithium nickelate and LiMn2O4.

3. lithium ion cell positive as claimed in claim 1, it is characterised in that described positive active material lithium from Weight/mass percentage composition in sub-anode is more than or equal to 90wt%.

4. lithium ion cell positive as claimed in claim 3, it is characterised in that described positive active material lithium from Weight/mass percentage composition in sub-anode is less than or equal to 99.9wt% more than or equal to 95wt%.

5. lithium ion cell positive as claimed in claim 1, it is characterised in that the length of the plurality of CNT Identical.

6. lithium ion cell positive as claimed in claim 1, it is characterised in that the surface of described CNT is pure Net surface.

7. lithium ion cell positive as claimed in claim 1, it is characterised in that described conductive carrier farther includes Carbon black pellet, this lithium ion cell positive is by positive active material particle, CNT and carbon black pellet group Become.

8. a lithium ion cell positive, it is characterised in that this lithium ion cell positive is by lithium ion cell positive activity Material grains and multiple CNT composition, the plurality of CNT intersects and is wound a network knot Structure, the surface of each CNT has viscosity, and this positive active material particle is attached to CNT Surface, described length of carbon nanotube is more than 200 microns, and described CNT is in lithium ion cell positive Weight/mass percentage composition is less than 10wt% more than or equal to 0.1wt%.

9. lithium ion cell positive as claimed in claim 8, it is characterised in that described network structure farther includes The one of graphite, acetylene black, carbon black and carbon fiber particles or any mixture.

10. lithium ion cell positive as claimed in claim 8, it is characterised in that described CNT is at lithium-ion electric Disordered uniform distribution in the positive pole of pond.

11. 1 kinds of lithium ion batteries, it is characterised in that this lithium ion battery includes as described in claim 1 to 10 one Lithium ion cell positive.

12. 1 metal ion species batteries, this metal ion battery includes a positive pole, it is characterised in that this positive pole is by just Pole active material and conductive carrier composition, this conductive carrier be between multiple CNT mutually be wound around or Person is be combined with each other by Van der Waals force and constitutes the network structure of an entirety, and described positive electrode active materials is distributed The network structure of CNT composition is adhered to by CNT or is wound around, described length of carbon nanotube More than 200 microns, weight/mass percentage composition in lithium ion cell positive for the described CNT is more than or equal to 0.1wt% is less than 10wt%.